I am a fan of high quality leather holsters and have found Kramers Horsehide about the best there is for OWB holsters.
As far as IWB holsters are concerned (and I am probably in the minority here) I like the inexpensive floppy soft suede IWB holsters the best. Yes, they will collapse after the gun has been drawn and you will need two hands to re-holster, but that has never been a major concern to me.
The soft suede type hosters are the thinnest, softest and most comfortable as far as I am concerned, and I have yet to find a stiff leather holster even somewhat comfortable to carry for IWB use. I carry a revolver and I have removed the clip from it's original position and re-located it so not to be directly in back of the cylinder. By doing so, it is better than original. Now they actually have them made that way from the Factory.